U.S. Pat. No. 4,261,173 issued Apr. 14, 1981, discloses a hot gas engine heater head for a multi-cylinder, double-acting hot gas engine in which each cylinder is surrounded by an annular regenerator unit and in which the top of each cylinder and its surrounding regenerator unit are interconnected by a heater head comprised of a plurality of heater tubes interconnecting the cylinder tops and surrounding regenerator unit tops, the individual heater heads being then arranged to form a single annular heater around a single combustor volume. For this purpose, arcuately-shaped manifolds are provided on the tops of the cylinders and of the annular regenerator units to form two complete concentrically disposed rings of arcuately-shaped manifolds. In U.S. Pat. No. 4,422,291 issued Dec. 27, 1983, a hot gas engine heater head construction for a multi-cylinder double acting hot gas engine is described in which each cylinder is surrounded by an annular regenerator unit and in which the tops of each cylinder and its surrounding regenerator are interconnected by a multiplicity of heater tubes fabricated in the manner disclosed in U.S. Pat. No. 4,261,173. In U.S. Pat. No. 4,422,291, the manifold assembly comprises a centrally disposed duct connected to the top of each cylinder and surrounded by a wider diameter annular-shaped duct connected between the opposite ends of the heater tubes and the regenerator unit. With this configuration, the manufacture of the manifolds and the joining of the heater tubes to the manifolds is simplified and makes it possible to use different materials in the components exposed to thermal stresses with a minimum of problems encountered with the necessary joints. U.S. Pat. No. 3,940,934 issued Mar. 2, 1976, describes a heater head construction for Stirling engines having an essentially V block wherein the cylinders, pistons, piston-rods, wrist pins, and connecting rods to the crankshaft for the cylinders in each bank of the V-shaped block are of the same length and identical construction so as to minimize the number of component parts required in the construction of the engine. An engine possessing these characteristics hereafter is referred to as an equal-V engine as opposed to previously known unequal V engines such as disclosed in FIG. 3 of U.S. Pat. No. 4,261,173 and in U.S. Pat. No. 4,417,443. However, the multi-cylinder, equal V engine disclosed in U.S. Pat. No. 3,940,934, while it does employ a single annular heater head cannot employ properly balanced arcuately-shaped manifolds and requires a plurality of regenerator canisters which are interspaced between the cylinders of the engine.
The prior art annular heater head in combination with arcuately shaped manifolds was recognized as being desirable. For example, the arcuately shaped manifolds provided for good flow distribution to the heater tubes. Heretofore, however, multi-cylinder, hot gas engines which attempted to combine the desirable annular multi-tube heater head, and the desirable arcuately-shaped manifolds to assist in achieving a balanced flow of working fluid through the heater tubes have not been entirely satisfactory because of the required engine complexity and resulting high production cost. For example, such an arrangement was possible with the multiple crankshaft, square cylinder formation engine shown in FIG. 1 of U.S. Pat. No. 4,261,173, or in the V-type engine requiring only a single crankshaft but only if the cylinders were arranged in an unequal V formation as shown in FIG. 3 of U.S. Pat. No. 4,261,173 and in U.S. Pat. No. 4,417,443.
The present invention for the first time provides a multi-cylinder, hot gas engine which is less expensive to produce than any known prior art configurations and which combines the desirable annular, multi-tube heater head, an annular regenerator, and arcuately shaped manifolds and achieves the desirable maximum average working fluid temperature for best engine operating efficiency, and employs a single crankshaft, equal V cylinder formation. In accordance with this invention, the arcuately-shaped manifolds can be formed in an optimum manner for flow distribution to the attached heater tubes by balancing and minimizing the lengths of the arcuate manifold between the cylinder and regenerator tops and the most distant of the heater tubes on the arcuate manifold. Accordingly, the present invention reduces manufacturing costs because of simpler machining of an equal V cylinder formation as contrasted to an unequal V cylinder formation, uses fewer engine parts, and achieves high engine operating efficiency. In order to reduce manufacturing costs, employ the desirable annular regenerator and annular multi-tube heater head and achieve good flow balance, the present invention was devised.